The present invention relates to a homogeneous bulky porous ceramic material, having adjustable and controlled porosity and pore diameter. The present ceramic porous body can be used for liquid filtration, gas separation, or for bringing fluids into contact as in catalytic reactions, or for emulsion production and other applications that use a ceramic porous material.
Numerous ceramic membranes are already known. They are generally formed by successively stacking layers on a support having large pores (macroporous support). The support gives the membrane its necessary mechanical strength. The stack of layers makes it possible to progressively reduce pore diameter. These layers are difficult to develop. The main characteristics of the filtration layer, in other words pore diameter and porosity (or porous volume), are also for a large part a function of the characteristics of the layer on which they are deposited, and this does not allow variation over a very extensive range. Additionally, their firing temperature needs to be below the firing temperature of the sub-layer. In some cases, this means a low firing temperature that is insufficient to allow optimal keying or bonding of the layer onto the sub-layer.
With this technique, filtration membrane manufacture is a long and costly procedure including a large number of steps; it does not make it possible to adapt membrane characteristics to the fluids to be filtered. On the other hand, porosity of the macroporous support is low to ensure sufficient mechanical strength when the membrane is in use. Finally, provision of a small-pore-diameter layer requires fairly low firing temperatures, such temperatures being insufficient to obtain the optimal properties for the material.
The present invention sets out to provide a homogeneous bulky porous ceramic material. More particularly the present invention sets out to provide a homogeneous bulky porous ceramic material having an average pore diameter D50 which preferalby is less than 4 xcexcm and of which the closed porosity is less than 4%, preferaby less than 2%. D50 is the volume equivalent average diameter such that 50% of the pores have a diameter less than D50.
According to one embodiment, the distribution of pore diameter expressed in terms of volume is that of a monodisperse system; in this embodiment, standard deviation, expressed as a percentage, of volume equivalent average diameter D50 is less than 35%, preferably less than 25%. Typically, the material according to the invention will have a standard deviation, expressed as a percentage, comprised between 10 and 25% of the volume equivalent average diameter D50.
According to one embodiment, the material of the invention has a bubble point corresponding to the pore diameter measured on said material. According to this embodiment, there is correspondence when the two values differ by less than 10%.
A first advantage of the present invention is that it provides a homogeneous bulky structure, in other words one that has the same pore diameter throughout the material thickness. The term xe2x80x9cbulkyxe2x80x9d has been chosen to distinguish this present material from a layer of small thickness; the characteristic dimension of the material is of the order of a millimeter, in other words the material is on a macroscopic scale. The term xe2x80x9chomogeneousxe2x80x9d is also designed to distinguish the material from a stack of successive layers which could possibly have a similar characteristic dimension.
A second advantage of the present invention is that of making it possible to adjust, in a simple fashion, the key characteristics of the membrane structure, in other words pore diameter and porosity, this being done in a simple and rapid manner, as well as over a wide range of variation without loss of mechanical strength. Such adaptability is obtained independently for pore diameter and porosity; in other words, both criteria can be adjusted independently one of the other. This adaptability is obtained without modifying the sintering temperature of the parts obtained.
A third advantage of the present invention is that of making it possible to obtain porous ceramic membranes that does not exhibit any structural defect.
A fourth advantage of the present invention is that it simplifies manufacture, due to eliminating, firstly, intermediate layer manufacture and, secondly, the need for end sealing.